Yes, that's it in a nutshell for dottybacks. There are a couple of exceptions you might consider (and bearing in mind that you may still encounter aggressive individuals that don't behave quite as you would like): Pseudochromis fridmani and P. sankeyi both live in groups rather than pairs or singletons in the wild. Even so, I wouldn't have more than a small group in a tank of that size. You might also consider getting a pair of P. cyanotaenia. I have even kept a pair of one of the larger species (Ogiblyina queenslandiae) in a 100 gallon tank without problems. They bred every couple of weeks ... and terrorised the other fish in the tank.